The present invention relates generally to tools of the type intended for performing drilling and allied operations and more particularly to such tools which are effective not only to drive a rotary cutting element but also to impact feed and return movements thereto with respect to a work piece.
Pressure fluid operated tools possess numerous features and make their employment especially advantageous in an almost infinite number of applications among which features are included their comparatively small size, light weight, durability, ease of control, and safety. Each of these features has contributed to the wide use of portable tools of this type in the so-called temporary tooling practice which has been widely adopted by industry where frequent design changes make uneconomical the utilization of permanent, special-purpose machine tools.
Many portable pressure fluid operated tools incorporate piston and cylinder arrangements for effecting longitudinal, or feed and return spindle movement. Examples of such tools can be found in U.S. Pat. Nos. 2,527,968; 2,643,555; and 4,329,092.
In the case of such tools for performing drilling and allied operations on conventional materials it has been found difficult to achieve linear forward thrust control for advancing the cutting tool into the work.
There has not been an adequate means to provide linear control of the thrust of such a device until the emergence of the present invention.